#include<stdio.h>

int Sum(n)
{
	int sum = 0;

	for (int i = 1; i <= n; ++i)
	{
		sum = sum + i;
	}
	return sum;
}

void main()
{
	int n;
	int sum = 0;
	scanf("%d", &n);
	sum = Sum(n);
	printf("%d\n", sum);
}